1. Field of the Invention
The present invention relates to a method for forming a wiring layer on a semiconductor substrate and more particularly to a method for forming a contact hole to ensure good quality of the wiring layer.
2. Description of the Prior Art
In general, there has been used a technique of contact hole formation in which gate electrodes, capacitors and the like are formed on a semiconductor substrate, and a CVD-SiO.sub.2 film having good coverage, or a PSG or BPSG film is used for a layer insulation film to be subjected to fellow by high-temperature annealing for flattening so that a contact hole is formed. In addition, there has been used a combination technique of isotropic etching and anisotropic etching as well as a taper etching technique and a contact reflow technique in order to improve the coverage of a sputtering metal to be used in the subsequent electrode formation.
In that case, it is necessary to precisely control quantity of isotropic etching so as not to come into contact with an electrode wire on a substrate. As a countermeasure, a high-resistance film such as a SiN film having a thickness of about 200 .ANG. is inserted into the underside of the layer insulation film such as the PSG or BPSG film so as to function as an etching barrier layer for isotropic etching by an etching solution having a capacity ratio of 10 (H.sub.2 O):1 (HF and NH.sub.4 F), i.e., BHF (buffered hydrofluoric acid).
Referring to the above-mentioned technique of contact hole formation, a contact hole 23 is formed on a semiconductor substrate 22 having gate electrodes 21 with a hood 24a of a SiN etching barrier layer 24 remaining therein as shown in FIG. 2. In that state, a metal is laminated and then wiring is patterned. A gate insulating film is indicated at 25, and a layer insulation film is indicated at 26 and 27.
In the process of removing a native oxide film which is to be performed after forming the contact hole 23 and before laminating the metal (a wet treatment by BHF having a mixing ratio of 100:1), only the SiN etching barrier layer is not etched so that the hood 24a remains as shown in FIG. 2. The coverage of the metal to be formed by a sputtering method is deteriorated owing to the hood 24a. In the extreme case, disconnection is caused.
It is an object of the present invention to provide a method for forming a wiring layer in which an etching barrier hood can be prevented from remaining in a contact hole even though a wet treatment is performed before metal deposition in the case where the contact hole is to be formed by means of an etching barrier layer.